“I got worms”: Soil-transmitted helminths digest

Infection-carrying worms can get into our bodies, set up shop in our intestines and suck our blood. This family of dangerous parasites, and the infection they carry, are the reason why there are children who are eating enough but are still malnourished.

Soil-transmitted helminths (helminth = parasitic worm), more commonly known as intenstinal worms, affect more people than any other neglected tropical disease. Up to 1.6 billion people worldwide are at risk of being infected by these nasty parasites, and the World Health Organisation estimates that 135,000 deaths a day are a result of these infections.

Each intestinal worm infection is defined by the type of worm which causes it. The three most common worms are: roundworm (Ascaris lumbricoides); whipworm (Trichuris trichiura); and the hookworms, (Ancylostoma duodenale and Necator americanus).

Worldwide, roundworm is by far the most widespread and recent estimates show that over one billion people are infected. Whipworms and hookworms affect around 795 million and 740 million people, respectively.

Intestinal worms thrive in warm, humid soil and spread when people come into contact with infected faeces. As a result, these diseases disproportionally affect the world’s poorest tropical and sub-tropical countries, where public health and sanitation standards are inadequate.

The worm journey

The worms’ infections are spread either by ingestion of eggs found in contaminated food (such as beans, rice, and various grains); or by baby worms piercing through the skin. Once inside, the parasites get into the intestine where they burrow into the surface. With one end secured and the tail free, they mate and do most of the damage.

A picture of the cycle of how the worm is transferred from the soil and into a person

As the eggs pass through the digestive system and out in faeces, the infection they carry can be passed on. As a result of poor living standards in developing counties, someone may defecate in an open space such as a garden or field; or faeces may be used as fertiliser – contaminating the soil.

If someone comes into contact with this tainted soil, also known as night soil, roundworm and whipworm can develop. Hookworm eggs are not infectious per-se but become so as they mature in the soil and hatch. The baby worms that comes out, larvae, can penetrate human skin. Hookworm infections normally begin when people walk barefoot on night soil.

The infected

A picture of a child with a swollen belly, full of worms (Picture from nazarethhouseap.org/)Severe infection by soil-transmitted helminths causes many disabling health effects on the sufferers. These are common to all types of helminth but may differ in severity between them. An initial worm invasion of up to 100 worms would not result in major health problems.

When adult worms get onto the intestine surface they dig themselves right in and suck on the host’s blood. Major blood loss can cause diarrhoea, abdominal pain, swelling, and weight loss that can lead to anorexia. Significant blood loss can also lead to iron-deficiency and a type of anaemia which means the blood cells which carry the oxygen around are very small. In children, this type of anaemia can also result in physical and mental retardation.

Deworming intervention

A number of ‘deworming’ schemes, particularly school-based ones, have been set up across the world to control the worm attacks.

The use of drugs has improved child health and development and free access to high quality medicines and preventative tools are advocated by the World Health Organisation. Albendazole, mebendazole and benzimidazoles are the three main drugs which are used, each with more importance for a different intestinal parasite.

The drugs target tubulin, a protein which strengthens cell structure and is part of the transport network between worm cells. The drugs directly damage the tubulin, making it impossible for the worm to produce energy and survive. This results in the gradual immobilisation and eventual death of the helminths.

Measuring prevalence and intensity of the worm infections, and their decline after drug administration gives an indication of the effectiveness of treatment. This long process can be done by studying stool samples of each patient.

The ease of reinfection, either by walking barefoot (allowing hookworm larvae to penetrate the skin) or by forgetting to wash your hands after a toilet break, means that simply providing drugs is not enough. Health education is crucial.

An added complication

New research highlights further difficulties faced by countries which already have limited health resources as they tackle soil-transmitted helminth infections.

The study suggests that children born to pregnant women who have been treated with soil-transmitted helminth drugs are at increased risk of having allergies such as asthma or eczema. This adds an extra problem to the developing countries which have limited health supplies. The effect of eczema can be particularly critical in low-income countries as skin irritation can lead to wounds developing, making patients more vulnerable to other infections.

Success story: Kenya

Kenya Medical Research Institute (KEMRI) has been tackling the country’s soil-transmitted helminth problem by investing their efforts in educating and treating schoolchildren. This has been made a bit easier by the introduction of free primary education, which has seen attendance rise and the quest to help the 8 million children at risk of infection much more effective.

Previous studies have shown children are one of the main sources of transmission, so directing intervention at them deals with the problem at its source. These health-aware children also educate their families, raising awareness of the infections and how it is prevented.

A child being washing her hands as part of a wider scheme of intestinal worm prevention in Kenya

KEMRI’s programme includes building latrines in schools and installing big water containers with taps outside each classroom to remind children and encourage them to wash their hands.

Dr Charles Mwandawiro, Assistant Director of KEMRI, said: “Our project [is] reaching up to 40 000 children…hookworm [has fallen] from 40-45 per cent to practically zero.”

Deworming programmes through schools like this have proved to be cost effective. In Kenya, where the healthcare budget is just $6 per person each year, price is crucial to success.

Projects similar to this, which abide by WHO guidelines for treating children, have also been reported in Cambodia and Uganda. These schemes are crucial for success in controlling and eradicating these killer worm infections.

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